High-strength ropes are used for many commercial and recreational purposes; many of which require long continuous lengths to perform the desired function. For example, applications such as deep sea moorings, deep shaft hoisting, deep-sea winching, tower cranes, aerial lifting or hoisting, and other applications. Many of these applications require a substantial length of rope to perform its function, and the self-weight of the rope may become excessive and hinder the ability to perform the desired function. Moreover, because many of these applications involve hoisting or lifting objects, it is desirable for these ropes to be torque-balanced; that is, the configuration of the lay of the individual wires comprising the rope strands and the twist of the rope strands in order to form the rope are substantially balanced such that the rope inherently resists rotating when a tension force is applied.
If the rope is not torque-balanced, the item being hoisted or lifted will just rotate in a circle which may introduce imbalance or other undesirable forces or movements. Many of the commercial applications utilize wire rope because it provides a high strength and sufficient ductility thereby allowing for a gradual and visual indication of failure or damage prior to actual failure. The ability to detect potential failures using non-destructive testing is paramount for many of these applications as it allows rope defects to be observed by operators and inspectors prior to the occurrence of an actual failure and thereby prevent accidents.
One persistent shortcoming in the art is that the weight of wire rope limits many applications because the wire rope itself weighs so much that it significantly works against the desired functionality of the application utilizing wire rope. One option available is to reduce the weight of the rope by using lighter-weight, high-strength synthetic fiber ropes. High-strength synthetic fiber ropes provide a desirable strength-to-weight ratio and may also be torque-balanced or rotation resistant. However, in any running rope applications wherein the rope has to be spooled on a multilayer drum or winch, synthetic ropes tend to perform poorly. Synthetic fiber ropes often fail in running rope applications because they lack the abrasion resistance and durability necessary. Further, synthetic fiber rope tends to flatten when it is wound under tension and thus, it is not ideal for multi-layer spooling applications. The continual abrasion and flattening out of wire rope when it is spooled on a drum or winch gradually breaks down the fibers thereby gradually reducing the strength of the rope. This reduction in strength is usually not detectable using non-destructive testing thereby leaving the condition of the rope unknown at any given time. If the actual strength of the rope decreases to a point that it is lower than the working stress required for the application, then a sudden failure may occur. Since the working stress is experienced when the rope is hoisting or otherwise being tensioned, a sudden failure of the wire rope would only occur when it is loaded and would put workers at risk and/or cause damage to the equipment being hoisted and surrounding property, or potentially many other undesirable and/or dangerous conditions.
There is a substantial need in the art for a reduced-weight torque-balanced rope that (i) provides the strength-to-weight ratio of high-strength synthetic rope, (ii) provides the tensile strength provided by wire rope or high-strength synthetic rope, (iii) is cut and abrasion resistant, and (iv) has the desired durability of wire rope for rope or tension members that are used in running-rope or other applications.